“Tilt-up” is a construction technique commonly used in constructing industrial-scale buildings such as warehouses. In tilt-up construction, an area of land is generally cleared of organic debris and other obstructions (e.g. boulders), and brought down to suitable elevation and grade. The land is checked to ensure that it is capable of supporting a building foundation. Footings lying around the perimeter of the area of land are poured. Wet concrete is then poured over the ground and allowed to set and form a concrete slab. The concrete slab forms the flooring of the building. To prevent surfaces bonding to the concrete slab, the concrete slab is sprayed with a chemically reactive bond breaker. Concrete elements such as walls (e.g. exterior walls) are then formed horizontally on top of the concrete slab by pouring wet concrete into a pre-defined area defined by a wood formwork. The wet concrete sets to form the concrete element. The wood formwork is removed, and the concrete element is then tilted to an upright position from a horizontal position and positioned at the perimeter of the concrete slab.
Exterior walls made for tilt-up construction generally comprise: (i) an exterior layer called a fascia wythe; (ii) an interior layer called a structural wythe; and (iii) insulating material therebetween. To form an exterior wall, welded wire mesh is laid within the pre-defined area defined by the wood formwork, and a first layer of wet concrete is poured over the welded wire mesh. This first layer of wet concrete sets and forms the fascia wythe. Before the first layer of wet concrete sets, insulating material is positioned over the first layer of wet concrete and coupled to the first layer of wet concrete by methods known in the art. For example, insulating material may be coupled to the fascia wythe via wythe ties (e.g. Thermomass® GFRP wythe ties). The insulating material is generally a non-weight bearing insulating material (e.g. extruded polystyrene insulation). Once the first layer of wet concrete has set, reinforcing bars are laid out over the insulating material, and a second layer of wet concrete is poured over the reinforcing bars and insulating material. The second layer of wet concrete is coupled to the insulating material by methods known in the art and sets to form the structural wythe. A construction crane may then be used to manoeuvre the exterior wall to its desired upright location and position.
Previously, building energy codes pertaining to industrial buildings did not require an exterior wall to be insulated. As such, it was common practice to have only the structural wythe as the exterior wall (i.e. no insulating material and no fascia wythe), and to mount fixtures directly onto the structural wythe. Fixtures include, but are not limited to, door frames, window frames venting grills or other building components.
Presently, many energy efficiency standards require the exterior walls of new industrial buildings (including “tilt-up” concrete buildings) to be insulated. In order to meet such standards, it is common to construct an exterior wall that comprises a fascia wythe and a structural wythe, wherein the two layers of wythe are separated by insulating material or a thermal break at all locations therebetween. Such an exterior wall is exemplified in FIG. 1(a), which shows a structural wythe 110 and a fascia wythe 120 of an exterior wall 100 separated by insulating material 130.
In practice, a fixture (e.g. a door frame) is mounted onto a side edge of the exterior wall such that the width of the fixture covers the insulating material that extends to the side edge of the exterior wall. The weight of the fixture is supported by the weight-bearing structural wythe. The fixture also acts as a barrier that reduces the loss of thermal energy where the insulating material meets the side edge of the exterior wall. As neither the insulating material nor the fascia wythe is weight-bearing, direct mounting of the fixture onto the insulating material or fascia wythe may result in structural failure over time. To improve the overlap between the fixture and the weight-bearing structural wythe, the shape of the insulating material and the shape of the structural wythe may be modified such that only a narrow rib of insulating material extends towards the side edge of the exterior wall. In this arrangement, and referring to FIG. 1(b), a fixture 140 may be mounted mainly to the structural wythe 110 while still covering surface 130a of the insulating material 130. However, because the fixture 140 still overlaps at least a portion of the non-weight-bearing insulating material 130 (i.e. over insulating material surface 130a), structural failure where the fixture overlaps with the non-weight-bearing insulating material may still occur over time.
To further provide weight-loading support to the fixture, a piece of wood 150 may be positioned between insulating material 130 and the side edge of the exterior wall as shown in FIG. 1(c). The wood 150 acts as a heat loss barrier and also provides a mounting and weight-bearing surface for fixture 140 to be mounted on. However, wood and concrete expand and contract at different rates, and the combination may eventually lead to mechanical failure. In addition, moisture may access the piece of wood, and may lead to wood rot over time.
Accessory items, for example but not limited to canopies, are sometimes required to be affixed to the sides of the exterior walls. Typically, the accessory item is directly mounted onto the fascia wythe with one or more suitable fasteners such as, but not limited to, a threaded rod (e.g. Type 304SS ⅜″ all-thread rods). The fastener typically penetrates through the fascia wythe, the insulating material, and partially through the structural wythe, thereby locking the structural wythe and fascia wythe together. Such locking of the structural wythe and fascia wythe together does not accommodate for the potential thermal expansions of the structural wythe or the fascia wythe through the seasons, and may lead to cracking of the structural wythe and/or fascia wythe over time.